The present invention relates to the communication of digital television signals, and more particularly to a bandwidth efficient scheme for enabling a digital television data stream to carry most types of data conventionally carried in the horizontal blanking interval (HBI) of an analog television signal. Such data is generally pulse amplitude modulated (PAM) data that is modulated onto the luminance of the HBI portion of the analog video waveform.
Digital transmission of television signals can deliver video and audio services of much higher quality than analog techniques. Digital transmission schemes are particularly advantageous for signals that are broadcast via a cable television network or by satellite to cable television affiliates and/or directly to home satellite television-receivers. It is expected that digital television transmitter and receiver systems will replace existing analog systems just as digital compact discs have replaced analog phonograph records in the audio industry.
One way to transmit the compressed video data to a receiver is in the form of packets contained within a packetized data stream. Typically, packets carrying compressed video data are multiplexed with other packets, e.g., carrying corresponding audio data and control information necessary to reconstruct a television signal. One standard for transporting digital television signals in this manner is the MPEG-2 standard, details of which can be found in the International Organisation for Standardisation, ISO/IEC 13818-1, International Standard, Nov. 13, 1994 entitled xe2x80x9cGeneric Coding of Moving Pictures and Associated Audio: Systems,xe2x80x9d recommendation H.222.0, incorporated herein by reference. Further details of the video syntax and semantics for MPEG-2 video can be found in International Organisation for Standardisation, ISO/IEC 13818-2, International Standard, 1995 entitled xe2x80x9cGeneric Coding of Moving Pictures and Associated Audio: Video,xe2x80x9d recommendation H.262, also incorporated herein by reference.
Another standard for transporting digital television data in a packet stream is the Advanced Television Systems Committee (ATSC) Digital Television Standard A/53, approved on April 12 and Sep. 15, 1995, incorporated herein by reference. The ATSC Digital Television Standard is based on the ISO/IEC MPEG-2 Video Standard, the Digital Audio Compression (AC-3) Standard, and the ISO/IEC MPEG-2 Systems Standard.
In the ATSC and MPEG-2 systems (and the similar DigiCipher(copyright) II system proprietary to General Instrument Corporation, the assignee hereof) a transport stream, or transport multiplex is made up of a contiguous set of fixed length packets. The video sequence is transported using a hierarchical structure in which a sequence header is followed by various extensions, user data, a group of pictures (xe2x80x9cGOPxe2x80x9d) header, optional user data, a picture header, etc. The sequence header provides information for a sequence of pictures, which in general will include more than one GOP. This information includes, for example, horizontal and vertical size values, aspect ratio, frame and bit rate, and quantization parameters for the video data. A user data extension can also be included which, among other things, provides additional data for use by decoders. The DigiCipher(copyright) II standard provides for the transport of additional user data after the sequence header, in order to identify a DigiCipher(copyright) II signal and the use of any special video compression techniques used within a sequence, including DigiCipher(copyright) special prediction and block motion estimation.
In both the MPEG-2 and DigiCipher(copyright) II syntaxes, a sequence display extension containing, e.g., video format and color description information, is provided in addition to the sequence extension and user data. A subsequent group of pictures header provides, among other information, a time code. Thereafter, a picture header is provided which includes various information pertaining to a corresponding picture in a sequence of pictures to be displayed. A picture extension and, ultimately, the actual picture data to be decoded and reproduced for viewing, is then provided. It is noted that MPEG does not specify the order in which various extensions (such as the sequence display extension) or the user data must be transmitted beyond the fact that they must be after the sequence extension and before the GOP header (if provided) or the picture header. MPEG does not require GOP headers to be sent, and such headers may be bypassed in particular implementations.
In a practical transmission system it may be necessary to include additional data at different times for specific purposes, such as controlling new features of a video appliance and peripherals for such appliances. Such additional data may be carried in the horizontal blanking interval (HBI) portions of an analog television signal, and is referred to herein as xe2x80x9cHBI user informationxe2x80x9d, xe2x80x9cuser dataxe2x80x9d, or xe2x80x9cuser information.xe2x80x9d
Many methods have been developed for services provided via waveforms carried in the HBI lines of analog and composite video. Digital video compression systems tend to employ algorithms optimized for the characteristics of two dimensional motion video. These algorithms are not generally well suited for the compression of video waveforms present in the HBI lines of analog video.
The character of HBI waveforms is very different compared to active video. Lack of compression for these lines is very bandwidth intensive, such as sending 8 or 10 bit samples of luminance and chrominance pixels. For example, 14 luminance and chrominance values at 8 bit resolution for 470 lines per frame and 30 frames per second requires 3,158,400 bps while the information conveyed by these lines only represents 14,100 bps for Microsoft""s Data Broadcasting Service. As the transition to digital video proceeds, the demand for carriage and reconstruction of HBI services continues. Digital video distribution systems are expected to reconstruct the HBI waveforms as well as the active video, even when digital video compression techniques are employed. Thus, there is a need for algorithms, syntax and semantics specifically for the compression of the HBI portion of the video lines that will allow an efficient and flexible alternative to developing HBI-waveform specific user data syntax and semantics.
It would be advantageous to provide a generic transport syntax and semantics for digital television data that would accommodate various types of HBI user information which may or may not be used at any given time. Such a scheme would enable the economical management of bandwidth while providing flexibility as to the transport of HBI user information. The present invention provides a transport method and apparatus enjoying the aforementioned advantages.
In accordance with the present invention, a method is provided for communicating, in a digital television data stream, user information of a type conventionally carried as pulse amplitude modulation (PAM) data in a horizontal blanking interval (HBI) waveform or video overscan region of an analog television signal. The digital television data stream transports data according to a convention that includes a user data syntax. Such conventions include, without limitation, the MPEG-2, ATSC and DigiCipher II digital television standards. In accordance with the method, the conventional user data syntax is supplemented with a line indicator value specifying the first horizontal television field line(s) in which user information is carried as PAM data in a counterpart analog television signal. The user data syntax is also supplemented with at least one timing reference value that defines a relationship between a symbol rate of the PAM data and a reference clock of the digital television data stream. The user data syntax is then supplemented with a user information field sufficient to carry the user information.
The user data syntax can be further supplemented with a start sample value. The start sample value is indicative of a sample point at which a transition into a first luminance (luma) PAM symbol is to commence in a counterpart television signal reconstructed from the digital television data stream.
The user data syntax can be further supplemented with a first amplitude value indicative of an amplitude at which HBI luminance PAM symbols are to appear in the counterpart television signal that is reconstructed from the digital television data stream.
The user data syntax can be further supplemented with a pulse shape value indicative of a pulse shape that is to be provided for the HBI Luminance PAM symbols in the counterpart television signal reconstructed from the digital television data stream. Moreover, the user data syntax can be supplemented with a field number indicative of a television field in which corresponding HBI data is to be inserted in the counterpart television signal reconstructed from the digital television data stream.
The user data syntax can also be supplemented with a second amplitude value indicative of a second amplitude level of the HBI luminance PAM symbols.
As indicated above, the user data syntax is supplemented with a timing reference value. This value can comprise a HBI Luminance PAM symbol clock increment value and a HBI Luminance PAM modulus value. The symbol clock increment and modulus values are related to the PAM symbol rate and the reference clock as follows:             increment      ⁢              xe2x80x83            ⁢      value              modulus      ⁢              xe2x80x83            ⁢      value        =            symbol      ⁢              xe2x80x83            ⁢      rate              reference      ⁢                        xe2x80x83                ⁢                  xe2x80x83                    ⁢      clock      
The count value can comprise a word count indicating an integer number of HBI Luminance PAM words that follow and a remainder count indicating a number of HBI Luminance PAM bits totaling less than a full HBI Luminance PAM word that follow. The syntax thereby provides an efficient use of bandwidth by enabling remainders of less than a full PAM word to be communicated. In a specific embodiment, such as an MPEG-2 or ATSC implementation, the HBI Luminance PAM words are each 22 bits in length, and the method comprises the further step of inserting a marker bit after each HBI Luminance PAM word to guard against a false MPEG start code. The user information can be carried according to the user data syntax as HBI Luminance PAM words and HBI Luminance PAM bits. Each HBI Luminance PAM word comprises a string of HBI Luminance PAM symbols with the first bit corresponding to a first HBI Luminance PAM symbol to be reconstructed on a video line as displayed from left to right and then top to bottom. Each HBI Luminance PAM bit represents one or part of an HBI Luminance PAM symbol to be reconstructed on the video line. The HBI Luminance PAM bits are provided in the order in which their symbols are to be reconstructed on the video line subsequent to symbols reconstructed from any HBI Luminance PAM words, as displayed from left to right and then top to bottom.
Receiver apparatus is provided for decoding, from a digital television data stream, user information of a type conventionally carried as PAM data in a horizontal blanking interval waveform or video overscan region of an analog television signal. The digital television data stream transports data according to a convention that includes a user data syntax. A syntax processor detects information carried in accordance with the user data syntax. Such information includes a first value identifying first horizontal television line(s) in which particular user information is carried in a counterpart television signal. A second value identifies a relationship between a PAM symbol rate of the counterpart television signal and a digital television data reference clock. A third value indicates an amount of user information carried in the digital television data stream. The information carried in accordance with the user data syntax also includes the actual user information to be conveyed. A reconstruction processor is responsive to the first, second and third values for formatting the user information into HBI PAM data. An HBI inserter is provided for inserting the HBI PAM data into, for example, a digital television signal from which an analog television signal can be reconstructed. Alternatively, such a digital television signal can be directly recorded or reproduced by a digital television appliance such as a video recorder or digital television.
In the illustrated embodiment, the syntax processor detects a start sample value indicative of a sample point at which a transition into a first PAM symbol is to commence on each line in the reconstructed television signal. The HBI inserter is responsive to the start sample value for inserting the PAM data into the reconstructed television signal. The syntax processor detects a first amplitude value indicative of an amplitude at which PAM symbols are to appear in the reconstructed television signal. The reconstruction processor is responsive to the first amplitude value to provide the HBI PAM data at the amplitude indicated by the first amplitude value.
The syntax processor of the illustrated embodiment detects a pulse shape value indicative of a pulse shape that is to be provided for the PAM symbols in the reconstructed television signal. The reconstruction processor is responsive to the pulse shape value to provide the HBI PAM data with the pulse shape indicated.
The syntax processor can further detect a field number indicative of a television field in which corresponding HBI data is to be inserted in the reconstructed television signal. The HBI inserter is responsive to the field number for inserting the corresponding HBI data into a proper field.
A second amplitude value can be provided for detection by the syntax processor. The second amplitude value is indicative of a second amplitude at which PAM symbols are to appear in the reconstructed television signal. In such an embodiment, the reconstruction processor is responsive to the first and second amplitude values to provide the HBI PAM data at the first and second amplitudes.